The auxiliary back pulling device is a very important one among the optional auxiliary devices on the trenchless drilling rig, which directly determines the success of the trenchless project sometimes. Based on the analysis of the current mainstream motor-assisted device, a hydro-cylinder assisted device was designed. A two-degree-of-freedom mechanism is used to allow the tooth-shaped part automatically to engage the rack of the drill mast first and then the cylinder to provide assistance. Automatic switching can be realized remotely; thus reducing labor and costs.